Examples of known substrates with high electrical resistivity “HR” substrates are disclosed in documents US 2006/0166451 and US 2007/0032040. Such known substrates generally comprise a top layer in which or on which high frequency devices will be formed, an insulating layer below the top layer and a high-resistivity support. In some instances, additional layers could be inserted between the insulating layer and the support to further improve the high electrical resistivity properties of the substrate.
Although known HR substrates are suitable for devices with improved performance because they provide reduced signal loss in the support or improved signal to noise ratio due to reduced crosstalk, they suffer from a major drawback: their cost can be high. This is partly due to the fact that known HR substrates incorporate high-resistivity supports that are priced at an elevated cost compared to traditional, non HR, supports. High cost is a particular concern when substrates will be used for fabrication of devices to be integrated into price sensitive products, such as consumer products telecom markets
The higher cost of HR supports often arises because their manufacture requires additional steps. In case of mono-crystalline silicon, such additional steps often involve multi-step and lengthy annealing to precipitate residual oxygen present in the support. Such additional steps can also include, e.g., forming an additional layer in-between the insulating layer and the support, or removing a surface layer of the support to further increase or preserve the high-resistivity of the substrate, or so forth.